Annealing furnace



' Dec. 27, 1932. I w. E. MOOREQET AL 1,892,112

ANNEALING FURNACE Filed Dec. 2, 1931 i 4 Sheets-Sheet 1 gwuento c wlzzmzf M re g4 ieoaye Jmepa m attocmq Dec. 27, 1932. w. E. MOORE ET AL 1,392,112

V ANNEALING FURNACE Filed Dec. 2, 1951 4 Sheets-Sheet 2 za 5E gwu+;tov 20:71:27) KN 61:02:96 ZS. Imam Dec. 27, 1932.

W. E. MOORE ET AL ANNEALING FURNACE Filed Dec. 2, 1931 4 Sheets-Sheet 3 Dec.27, 1932. I 'w, MOORE A 1,892,112

A NNEALING FURNAC E Filed Dec. 2, 19;]. 4 Sheets-Sheet 4 'gmanto'c Z15" William! 5: H

7 660196 L Jimpaom Patented Dec. 27, 1932 UNITED STATES PATENT OFFICE WILLIAM E. MOORE, OF PITTSBURGH, AND GEORGE I. SIMPSON, OF CORLOPOLIB, PINN- SYLVANIA, ASSIGNOBS '10 PITTSBURGH RESEARCH CORPORATION, OF PITTSBURGH,

PENNSYLVANIA ANNEALING rumucn Application filed December 2, 1931. Serial No. 578,582.

Our invention relates to improvements in furnaces for heat treating operations and to a method of operating said furnaces,

Animportant object of our invention is the provision of means for controlling the atmosphere in heat treating furnaces.

Another object of our invention is to pro= vide means for excluding the outside atmosphere from the interior of the furnace.

A further object of our invention is to provide means to protect the furnace walls from the atmosphere maintained about the charge.

Still another object of our invention is to provide novel means for admitting the desired atmosphere to the furnace interior and to the charge, and for removing atmosphere from the interior of the furnace and from the charge.

A still further object of our invention is to provide a method and apparatus for changing the atmosphere of the furnace or of the charge with the least possible loss of gas and time.

Yet another object of our invention is the provision of a novel shield for'the furnace charge, and improved sealing means therefor.

Other objects and advantages of our invention will be apparent during the course of the following description.

In the accompanying drawings which form a part of this specification and wherein like characters of reference denote like or corresponding parts throughout'the same,

Figure 1 is a vertical sectional view of one form of furnace embodying our invention,

Figure 2 is a sectional view of a shield having an alternative form of sealing means,

Figure 3 is a sectional view of a furnace embodying a modified form of our invention,

Figure 4 is a similar view showing another form of our invention,

Figure 5 is a sectional view of a furnace embodying our invention in which an automatic pressure regulator is used,

Figure 6 is a longitudinal sectional view of a furnace having means for admitting gas to the interior thereof,

Figure 7 is a sectional view of a furnace having a novel shield and packing, I

Figure 8 is a similar view showing an automatic control valve on the shield, and,

Figure-9 is a detail view of a modified form of shleld cover.

In the drawings, wherein for the purpose of illustration is shown a preferred embodiment of our invention, the numeral 10 designates a furnace hood having a base 11 extending through the bottom thereof. Sealing means 12 are interposed between the base and furnace hood, and the roof of the hood is preferably, althou h not necessarily, removable. The particlfiar furnace structure and the heating means therefor form no part of the present invention and are shown more or lessdiagrammatically in the several views. Other t es of furnaces may obviously .be employeil In. the form of the invention shown in Figure 1, the charge 13 is stacked upon the hearth 11 which is referably covered on its top with a metal p ate 14. A metal shield or container 15 is arranged over the charge 13 and rests upon the plate 14. Any suitable sealing means may be provided between the hearth plate 14 and the shield. In Figure 1 we have shown a heat resistant gasket 16 arranged in a matrix or ve extending around the shield. Thega etextends below the bottom of the shield and is preferably circular in cross section, although other shapes may be used. The weight of the shield 15 forces the gasket into intimate contact with the plate 14 and effectively seals the interior of the shield from the rest of the furnace.

It is therefore desirable to remove these lib- 'erated gases from the vicinity of the metals beiwig treated.

e have found that it is a distinct improvement to provide one or more controllable exits for the gases so that a flow of some desired gaseous atmosphere may be swept throu h the furnace or container to carry I out 0 contact with the charge any of the gases which may have been liberated from the charge during heating.

The base and cover may be provided with gas inlets and outlets, and in Figure 1 we have shown, valved pipes 17 extending through the walls-ofthe hood 10 adjacent its top and bottom. Gas may flow continuously through the furnace hood and be controlled by the valves in the pipes 17. When the shield 15 is used, gas is admitted through the pipe 18 which extends up through the base, i'nteriorly of the shield. The shield isvented through its top by means of either of two valved pipes 19 and 20. Vent 19 extends to a point adjacent the lower end of the shield, while vent 20 terminates adjacent the top of the shield.

When gas is admitted through pipe 18 it is desirable to remove the air or other atmosphere in the shield, and if this atmosphere is lighter than the incoming gas it is vented through pipe 20, whereas if it is heavier than the incoming gas it is vented from the hot the shield through pipe 19. With 'angement, the incoming gas tends to rote. the atmosphere from the shield without becoming intimately mixed therewith, consequently the shield may be filled in a short time and with a relatively small loss of the incoming gas.

When the shield 15 is being used, and it is desired to prevent any leakage of gas therefrom, the pipes 1? may be utilized in building up a pressure in the furnace hood to equal or slightly exceed the pressure within the shield. This situation is desirable in cases where the gas used in the shield would attack the lining of the hood. The same result can also be'obtained, in some cases, by controlling the pressure within the shield relative to the normal atmospheric pressure in the furnace hood. This may be carried out by having the pressure within the shield equal to atmospheric or other pressure within the furnace, or slightly exceeding atmospheric pressure, to prevent entrance of the v furnace atmosphere, or slightly under atmospheric or other pressure within the fur nace to prevent escape of gas from the shield.

When the'heatin'g operation'is completed, the hood 10 with its heating elements 21 may be removed and the charge allowed to cool down under the protecting shield 15 and in the desired atmosphere. When a flow of atmosphere is maintained by leaving one of the exits open and continually admitting gas to the shield, the exits are closed when the hood 10 is removed, to maintain a constant atmosphere in the shield during the cooling down period and to prevent the entrance of air to the shield.

1 A. pipe 22 may extend throu h the base 11 to allow a thermocouple 23 to e inserted in the charge interiorly of the shield, and a seal may be provided in the an oil or liquid 23'.

In Figure 2 the base plate 14' is provided with upturned flanges 24 at its edges. The

shield 15' fits within these flanges and is spaced therefrom. A sand or other seal 16 may be arranged in the space between the flanges 24 and the shield 15'.

In the form of our invention shown in Fig"- ure 3 the base plate 14; is provided with upturned outwardly inclined flanges 24:"which serve as guides for the shield 15 when it is lowered into position on the base.

In filling a shield or furnace with gas, a large waste of gas has heretofore been experienced due to the turbulence caused by the entrance of the gas into the furnace atmosphere, and the consequent mixing of-the gas with the atmosphere.- This difficulty may e overcome by the construction shown in Figure 3 in which the gas used is lighter than the normal atmosphere, as for example, ammonia gas. The gas is admitted at the top of the chamber in such manner as not to create turbulence and consequentmixing with the atmosphere. The gas is admitted through a relatively small pipe 25 which extends through the base 11 and into the end of a larger inlet pipe 26 carried by the shield 15.. A depression 27 in the base allows the use of pipe 22 by means of a seal at the juncture of the pipes 25 and 26. i

- pipe 26 and its velocity is greatly reduced by the flared end 28 where it enters the shield chamber. The gas fills the upper portion of the chamber and forces the normal atmosphere out of the chamber between the shield and the base plate, as indicated by the arrows. There is very little turbulence and mixing, and a large saving of the gas is effected.

In Figure 4. is shown a construction suitable for use when the gas used is heavier than the normal atmosphere; In this case it is desirable to displace the residual atmosphere upwardly with as little mixture with the incoming gas as possible. The base plate 14 is provided with upstanding flanges 21, as in Figure 2, and the shield 29 rests on the base plate in spaced re lation with the flanges 24. A suitable sealing materialsuch as'sand may be arranged in the space between the shield and the flange, although other forms of seals may obviously be used. The upper end of the shield is open and provided with a channel 30 extending about the walls thereof. A cover 31 has a dependthe chamber-through enlarged or flared openlet valve adjusted with the outlet valve-32 in Figure 4 or 34 in Figure 3 to maintain the ,ing' lip or a. which rests in the channel 30;

shield 29-and has its end flared. The gas is admitted through pipe 25' and displaces the residual atmosphere which leaks out between the cover flange and the channel 30 as indi-' cated by the arrows. The displaced atmosphere can escape from the furnace hood through the flared, valved exit 32 in the top of the hood, or through one of the .other pi 's.

It will be seen, then, that to prevent tur 1'1- lence andmixin ofthe incoming gas with the residual atmosp ere, gas heavier than the residual atmosphere is admitted atthebottom of ings while gas lighter than the residual atmosphere is admitted through a flared opening at the top of the chamber. Where a shield isused,'the pressure of the gas within the shield is adjusted with relation to the atmos here in the furnace hood to prevent escape o the gas from the shield or to prevent entrance-of the hood atmosphere to the shieldchamber. The shield may be dispensed with entirely, and the as admtted directly to the furnace hood. Where no shield is used, and the hood is not sealed gas-tight, the desired adjustment of the furnace atmosphere relative to the outside atmosphere may be made to prevent escape of the furnace atmosphere or entrance of the out side atmosphere.

In place of relying upon the escape of the atmosphere or gas between the parts, such as the shield and base plate, or the shield cover and channel, openings may be provided for this purpose as seen at 57 in Figure 9. In place of adjusting the atmosphere within the shield to the furnace atmosphere, the furnace atmosphere may be adjusted relative to the atmosphere in the shield chamber, as by means of the valve pipes 33 in Figure 4.

In practice, the shield may be lowered over the pack of material on the hearth. The desired atmosphereis introduced through the flared inlet opening, and displaces the residual air which leaks out of the shield as shown in Figures 3 and 4. The furnace heating cov-- er 10 is then lowered into position and t e indesired pressure within the furnace chamher, which may be equal to or slightly above the atmospheric pressure on the shield. As

the furnace heats up and the atmospheres ex-' pand, the external and internal pressures are so regulated as to prevent the atmosphere in the shield from entering the furnace chamber. This is desirable in'cases wherethegas used will attack the refractory material of the furnace walls.

Where the atmosphere used does not have this deleterious effect, no precaution need be taken to ad 'ust the pressures, the. excess the inner s ield merely leaking out into the furnaoe'chamber, and passing out to the ex ternal atmosphere through pipe-32 in Figure 4 or 34 in Figure 3.

Whether or not a shield should be useddepends upon the materials treated and the atmospheres used. Where the atmospheres will react uFon the metal shield, no shield is used, as or example, in nitriding crank shafts where ammonia gas is used, it has been found that theuse of a metal shield unfavorably affects the operation due to the action of the ammonia on the metal shield, which resilts in the treated work being less hard, an

ammonia than when no metal is exposedto' the atmosphere used. It is desirable to enuiring the use of larger amounts of close the charge in a shield where the atmospheres used will attack the furnace walls, or where it is desired to cool'the work in a controlled atmosphere, while at the same time removing the heating hood for additional work.

' The use of one or more gas inlets so designed as to reduce to a minimum the tendency for the incoming gas to mix with the air in the shield has roved to be a very valuable expedient, and? has saved much time and gas in actual practice. If the gas is admitted through the usual pipes, there is a high velocity and the incoming gas is thoroughly stirred into the air already in the shield or furnace. Complete displacement of the residual'air can only be accomplished by venting a large quantity of this mixture, which entails a great loss of the incoming gas. On

the other-hand, if the desired atmosphere is introduced without turbulence and at a reduced velocity, there is very little disturbance in the residual air,and the full effect of the density difference of the two atmos pheres is obtained 'in clearing the shield of air and replacing it with the desired atmosphere with a minimum waste of the incommg gas. Gases such as ammonia, hydrogen and helium are introduced at the top of the container. Heavy ases such as carbon dioxide, nitrogen and t e like are introduced at ghee bottom of the container or furnace cham- In Figure 5 is shown a'furna'ce having an automatic control of the differential pressure between the atmospheres in the furnace and in the shield. Higher than normal pressures mayibe maintained in the shield without leakage by applying this pressure control. As sand seals are not absolutely gas tight, liquid or compound seals should be used at 12 between the base and furnace hood.

, 1 The furnace construction shown in Figure 5 is similar to that illustrated in "Figure 3, although other forms of shields and gas in- 35 has a flared end extending through the base and communicating with the interior of the shield, and gas enters theshield through the pipes 25, 26 and flared end- 28. An inlet pipe 36 communicates with the upper portion ofthe furnace hood and an outlet pipe 37 communicates with the lower por tion of the furnace hood.

The outlet pipe. 35 communicates with a pressure responsive device illustrated diagrammatically at 38 and the outlet pipe 37 communicates-with a pressure responsive device illustrated diagrammatically at 39. A. valve 40 in the inlet pipe 36 is operatively connected to the device 38 by a bar 41 and a valve 42 in the inlet pipe is connected to the device 39 by a bar 43. A. lever 44 is pivoted at its center and is connected adjacent its ends to the bars 41 and 43. Adjustment is secured b adjusting the connection between the'va ve arms and the bars 41 and 43 which are provided with a plurality of connecting openings for this purpose. Pressure in the shield operates through pipe and dem'ce 38 to control the inlet valve to the furnace chamber, and pressure in the furnace chamber operates through pipe 37 and device 39 to control inlet valve 42 to the shield .chamber. It will be seen, therefore, that a constant pressure difference may be maintained automatically in the two chambers by means of the pressure responsive devices 38 and 39 which also affect one another through the pivoted lever 44. This construction operates automatically, and overcomes pressure differences caused by heating and cooling, and by escape of atmosphere from one chamber to the otherl In Figure 6 is shown afurnace construction for admitting gas to a furnace chamber without causing turbulence and mixing of the incoming gas with the furnace atmosphere. The gas conduit communicates with a manifold 45 which communicates with a plurality of diffuser nozzles 47 in the top of the furnace hood. The displaced air escapes at the bottom of the furnace in any suitable manner, as

by means of a plurality of valved outlets 48. This arrangement of a plurality of diffuser nozzles connected by a manifold may be used with any of the furnaces shown, and located in the furnace hood or in the base for use with or without a shield. This construction is highly desirable when dealing with gases such as hydrogen or natural gases which form explosive mixtures with air. As mixing is reduced to a minimum, the time required for thoroughly gassing out the chamber, for tuming on the power without danger of an explosion due to the presence of residual air, is greatly reduced. Rapid gassing out of. a shield is also facilitated by the construction shown in Figures 3 and 4 in which the residual atmosphere escapes about the entire edge of the shield, at the top in Figure 4 and at the bottom of the shield in Figure 3, and consequentl is not delayed'in its escape.

In igure 7 is shown a furnace in which the base 14 is provided with an upstanding lip or flange 24 similar'to that shown in Figures 2 and 4. The shield 49 is provided with an inverted channel 50 around its lower edge which receives a gasket 51. The gasket terminates short of the lower edge of the channel 50 and rests on the lip 24 which extends up into the channel, the weight of the shield forcing the gasket into intimate contact with the lip '24.

The gasket seal shown in Figure 7 is superior to. the usual sand seal in that it permits uniform heating of the shield and base plate. The sand seal usually employed is open to the objection that it acts as a heat insulator and keeps the lower edge of the shield at a lower temperature than the top of the shield, and the consequent unequal expansion results in twisting and warping of the shield. With the uniform temperature present in the shield 49, there is no tendency to warping of the shield, as the lower edge of the shield is exposed directly to the heat of the resistor 21.

In Figure 8 the shield is similar to'that shown in Figure 7 although other types of shields may obviously be used. Gas is admitted to the shield through inlet pipe 25 and discharged fromthe furnace through valved pipe 33. An opening 52 is arranged in the top of the shield and allows the escape of gases from the shield chamber into the furnace chamber. A valve 53 normally closes the opening 52 and is supported by one arm of a bell crank lever 54 pivoted at 55 to the top of the shield. A plate or trigger 56 is secured to the underside of the furnace roof and engages the other arm of the lever 54. The weight of the valve normally maintains its closed position over the opening 52. When the furnace hood 10 is lowered onto the base 11, the trigger 56 engages the bell crank lever and raises thevalve into the open position shown in Figure 8. v In this position, gases may escape from the shield. When the heating period is over and the hood 10 is removed, the weight of the valve automatically closes it, and air is prevented from entering the shield. This construction obviates the difficulties encountered when a gas tight shield was used, in which accumulated moisture and obnoxious gases caused staining or scaling of the sheets during the cooling down period. With the present construction, however, moisture, steam and obnoxious gases are. released during the heating period but the shield is automatically sealed when the heating hood is removed." 1 v The valve 53 may be made of heat resisting material and may be provided with a gasket if desired. I

Although we have described our invention as applie to heat treating and annealing oppreferred embodiment of our invention it is 6 to be understood that various changes in the said size, shape and arrangement of parts, and in p the steps of our method may be resorted to without departing from the spirit of our invention or the scope of the subjoined claims.

Having thus described our invention, what we claim and desire to protect by Letters Patent is:

' 1. In a heat treating furnace, a base, a

rest on said base, said shield having a groove carried at its lower edge, and a gasket arranged in said groove and adapted to engage said base.

2. In a heat treating furnace, a hea hood, a base therefor, a base plate arran on said base, a shield adapted to rest on said base plate, said shield having a groove carried at its lower edge, and a gasket arranged in plate.

, 3. In a heat treating furnace, a baseed to rest on said plate in spaced relation, tothe upturned edges, and a sealing material arranged between the shield and the upturned edges of the base plate.

4. In a heat treating furnace, a base plate, a shield adapted to rest thereon, said shield having a. groove carried at its lower edge, and

verted channel around its lower edge, and a' a gasket arranged in said groove and extending therebelow, said gasket being adapted to engage the base plate. r a

5. In a heat treating furnace, a base adapted to receive a charge, a heatin hood therefor,,a base plate on said base having upturned edges, a shield adapted to be arranged over said charge and rest on said base plate, and sealing means between the upturned edges of the base plate and the shield.

plate having an upturned flange therearound, a shield therefor, said shield having an in gasket in said channel adapted to engage the upturned flange of the base plate.

7 In a heat treating furnace, a base plate having an upturned flange therearound, a shield therefor, said shield having an inverted channel around its lower edge, and a gasket in said channel adapted to enga e the up-v turned flange of the ase late an terminat: ing short of the lower e of the inverted channel, whereby the base ange extends into said channel to engage the gasket.

' 8. In a heat treating furnace, anbase, a remoyable heating hood therefor, a shield arranged within said hood, and a valve-controlled opening in said shield, j

. 9. In a heat-treating furnace, a base, a removable heating hood therefor, a shield arheating hood therefor, a shield adapted to groove and adapted to engage said base' 6. In av heat treating furnace, .a baseheating hood for said base, a shield arranged on said base and adapted to cover said charge,

said shield ha ano nin therein avalve pivoted to th e iield aid ormally closing said openin and means operated by the placement o the hood on the base to move the valve about its pivot to uncover the opening in the shield.

11. In a heat. treating furnace, a base adaptedto support a charge, a removable heating hood for said base, a shield arranged on said base and adapted to cover the charge, said shield having an opening therein, a lever pivoted intermediate its ends tothe shield, -a valve carried by said lever and adapted to normally close said opening, and means on the heating hood to engage said lever and move the valve away from the opening.

12. In a heat treating furnace, a base adapted to support a charge, a removable heating hood for said base, a shield arranged on said base and adapted to cover. the charge, sealing means between the base and shield, means to admit a gaseous atmosphere to said shield, said shield having an opening therein, means normally covering said opening, and means operated by the placing of the hood on the base to uncover said opening.

13. In a heat treating furnace, a base adapted to receive a charge, an open top shield arranged over said charge and resting on said base, said shield being adapted to receive a gaseous atmosphere and having a channel arranged'a'bout its upper end, and a shield cover having a depending lip adapted to rest in said channel and having openings adjacent the lower edge thereof to form a tortuous outlet for the gaseous atmosphere in said shield. V

14. In a heat treating furnace, a base, a heating hood therefor, means to admit a gaseous atmosphere to said hood, and means to gradually and progressively reduce the velocity and diffuse the incoming atmosphere as it enters the hood to reduce turbulence and heating hood therefor, and means to admit a gaseous atmosphere to said hood comprising a gas inlet pipe communicating with the 7 interior of the hood,'said pipe having its end progressively enlarged as it approaches the interior of the hood.

16. In a heat'treatin furnace, means to I admit a gaseous atmosp ere to the furnace comprising a gas inlet pipe having a gradulally and progre$ively enlarged and flared diffuser nozzle communicating with the interior of the furnace, and means of exit for the residual atmosphere displaced by the incoming gaseous atmos here. 4

' 17. In a heat treating furnace, means'to admit a gaseous atmosphere 'to the furnace comprising a plurality of flared diffuser nozzles communicating with the interior of the furnace, a manifold connecting the diffuser nozzles, and a gas conduit communicating with the manifold.

18. In a heat treating furnace, means to admit a gaseous atmosphere to the furnace comprising a plurality of flared diffuser nozzles communicating with the interior of the furnace, a manifold connecting the diffuser nozzles, a gas conduit communicating with the manifold, and means to permit the esca e of the residual atmosphere displaced by .t e incoming atmosphere. 19. In theoperation ofa. heat treating furnace, the method of gassing out the furnace'which comprises displacing the residual atmosphere in the furnace by forcin a gaseous atmosphere into the furnace w ile substantially preventing mixture of the gaseous atmosphere with the residual atmosphere.

20. In the operation of a heat treating furnace, the method of gassing out the furnace which comprises admitting a gaseous atmosphere to said furnace, gradually and progressively reducing the velocity of the gaseous atmosphere as it enters the furnace and removin the. displaced residual atmosphere.

21. the operation of a heat treating fur- V nace, the method of gassing out the furnace which comprises admitting a gaseous atmosphere to said furnace to displace the residual atmosphere of the furnace and progressively phere as it enters the furnace.

22. In the operation of a heat treating furnace having a charge container therein, the method of replacing the atmosphere in the charge container which comprises admitting a gaseous atmosphere to said container, while permitting the escape of the displaced residual atmosphere from the container and while substantially preventing turbulence and mixture of the incoming gaseous atmosphere with the residual atmosphere.

23. In the operation of a heat treating fur.- nace having a'charge container therein, the method of replacing the atmosphere in the charge container which comprises admitting a gaseous atmosphere to the container, and

gradually and progressively reducin the velocity of the gaseous atmosphere as it enters the container, while permitting the escape of the dis laced residual atmosphere.

24. n the operation of a heat treating furnace, the method of replacing the residual atmosphere with a. heavier gaseous atmosphere which comprises admitting the heavier gaseous atmosphere adjacent the bottom of reducing the velocity of the gaseous atmos the furnace and allowing.the displaced residual atmosphere to escape -adjacentthe top of the furnace.

25. In the operation of a heat treating furnace, the method of replacing the residual atmosphere of thefurnace with a heavier gaseous atmosphere which comprises admitting the heavier gaseous atmosphere at a low velocity and in a substantially diffused condition to the lower portion 'of the furnace, while permit-tin the escape of the displaced residual atmosp ere from the upper portion of the furnace.

26. In the operation of a heat treating furnace, having a charge container therein, the method of-re lacing the residual atmosphere of the container with a heavier gaseous atmosphere which comprises admitting the heavier atmosphere at a low velocity to the lower portion of the container while permitting the escape of the displaced residual atmosphere from the upper portion of the container. I

27. In the operation of a heat treating fur-v nace, the method of replacing the residual atmosphere. with a lighter gaseous atmosphere which comprises admitting the lighter gaseous'atmosphere to the upper portion of the furnace while permitting the escape of the displaced residual atmosphere from the lower portion of the furnace.

7 28. In the operation of a heat treating furnace, the method of replacing the residual atmosphere of the furnace with a lighter gaseous atmosphere which comprises admitting the lighter gaseous atmosphere at a low velocity and in a substantially diffused condition to the upper portion of the furnace while permitting the escape of the displaced residual atmosphere from the lower portion of the furnace.

29. In the operation of a heat treating furnace having a charge container therein, the

method of replacing the residual atmosphere of the container with a lighter gaseous atmosphere which comprises admitting the lighter atmosphere at a low velocity to the upper portion of the container while rmitting the escape of the displaced resi ual atmosphere from the lower portion of the container. j I

30. In the operation of a. heat treating furnace, the method of treating a charge which consists in continuously flowing a gaseous atmosphere past the charge during the heating Ian period, and maintaining a substantially constant atmosphere about the charge during the cooling period. t

31. In the operation of a heat treating furnace, the method of treating a charge which comprises supplying a gaseous atmosphere to the furnace, and mamtaining'a substantially constant pressure difference between the furnace atmosphere and the outside atmosphere.

32. In the operation of a heat treating furnace having a charge container therein, the method of treating a charge which comprises supplying a gaseous atmosphere to the charge container, and maintaining a substantially constantpressure difierence between the atmosphere of the container and the furnace atmosphere.

33. In the operation of a heat treating furnace having a charge container therein, the method of treating a charge which comprises supplying a gaseous atmosphere to the contuner, and controlling the container atmos phere and the furnace atmosphere to maintain a substantially constant pressure difierence therebetween.

34. In a, heat treating'furnace having a I charge container therein, means to supply a gaseous atmosphere to the container, and means to control the pressure difierence between the container atmosphere and the furnace atmosphere.

35. In a heat treating furnace having a charge container therein, means to supply a gaseous atmosphere to the container, means to control the furnace atmosphere, and means to control the pressure diflerence between the container atmosphere and the furnace at- 1 mosphere.

36. In a heat treating furnace having a charge container therein, means to supply a gaseous atmosphere to the container, means to supply a gaseous atmos here; to the f11rnace, and pressure operate means to control the pressure difference between the container atmosphere and the furnace atmosphere.

In testimony whereof we aflix our signa tures.

WILLIAM E. MOORE. GEORGE L. SIMPSON. 

